Unsaturated polyurethanes degradable by conjugate substitution reactions with amines and carboxylate anions

Main-chain scission of polymers induces a significant decrease in molecular weight and accompanying changes in physical properties and is important for applications in materials engineering, such as in photoresists and adhesive dismantling. In this study, we focused on methacrylates substituted with carbamate groups at the allylic positions for the purpose of developing a mechanism that efficiently cleaves the main chain in response to chemical stimuli. Dimethacrylates substituted with hydroxy groups at the allylic positions were synthesized by the Morita–Baylis–Hillman reaction of diacrylates and aldehydes. The polyaddition with diisocyanates afforded a series of poly(conjugated ester-urethane)s. These polymers underwent a conjugate substitution reaction with diethylamine or acetate anion at 25 °C, resulting in main-chain scission accompanied by decarboxylation. A side reaction by the re-attack of the liberated amine end to the methacrylate skeleton proceeded, whereas it was suppressed for the polymers with an allylic substitute of the phenyl group. Therefore, the methacrylate skeleton substituted with phenyl and carbamate groups at the allylic position is an excellent decomposition point that induces selective and quantitative main-chain scission with weak nucleophiles, such as carboxylate anions.


poly(tetrahydrofuran) (9)
Trifluoromethanesulfonic anhydride (1.01 mL, 6.15 mmol) was added dropwise to dehydrated tetrahydrofuran (100 mL, 1.23 mol) under nitrogen atmosphere. The reaction mixture was stirred at room temperature. After stirring for 3 min, water (2 mL) was added into the reaction mixture to stop the reaction. The obtained products were added to dry-ice methanol bath to precipitate polymer. The formed precipitates were collected by decantation then were dried under reduced pressure to give 9. Yield, 2.60 g (7.7%). M n = 1100, Ð = 1.85.
Polyurethane elastomer (P3b/6a/9) by prepolymer method To a solution of 9 (765 mg, 0.695 mmol) in dehydrated N,N-dimethylformamide (1.0 mL) under argon atmosphere, 6a (220 mg, 0.880 mmol), and di-n-butyltin dilaurate (catalytic amount) was added. The reaction mixture was stirred at room temperature. After stirring for 24 h, a solution of 3b (52 mg, 0.181 mmol) and di-n-butyltin dilaurate (catalytic amount) in dehydrated N,N-dimethylformamide (1.0 mL) was added to the reaction mixture. The reaction mixture was stirred further 24 h. After the reaction, hexane (40 mL) was added into the reaction mixture to precipitate polymer. The formed precipitates were collected by centrifugation then were dried under reduced pressure to give P3b/6a/9. Yield, 1.33 g (45%).

Main chain-scission
A typical chain-scission procedure is as follows. To a solution of P3a/6a (100 mg, 0.392 mmol for methacrylate moieties) in N,N-dimethylformamide (0.2 mL), a solution of diethylamine (equimolar to the methacrylate moieties) in N,Ndimethylformamide (0.2 mL) was added. The reaction mixture was stirred for 24 h at room temperature. After the reaction, 1 H NMR and SEC measurements for obtained product were performed to confirm chain-scission reaction.
Chain-scission of other polyurethanes using diethylamine and tetrabutylammonium acetate as nucleophile were performed following the above methods.

Model reaction using methacrylate and aniline
A typical model reaction procedure is as follows. To a solution of 10a (100 mg, 0.426 mmol) in N,N-dimethylformamide (0.2 mL), a solution of aniline (equimolar to the methacrylate) in N,N-dimethylformamide (0.2 mL) was added. The reaction mixture was stirred for 24 h at room temperature. After the reaction, 1 H NMR measurement for obtained product was performed to confirm chain-scission reaction. Model reaction using another methacrylate (10c) was performed following the above methods.        Fig. S10. 1 H NMR spectra (400 MHz, DMSO-d 6 , 298 K) (A) and SEC traces (0.01 M LiBr in DMF; 0.8 mL min −1 ; 40 °C) (B) before and after the degradation of P3c/6a using Et 2 NH. P3c/6a was prepared in a different lot from that in Table 4, Entry 4.   in DMF; 0.8 mL min −1 ; 40 °C) (B) before and after the degradation of P3c/6a using Bu 4 N + · -OAc. P3c/6a was prepared in a different lot from that in Table 4, Entry 4.